1. Field of the Invention
The present invention relates to devices useful for releasably restraining movement of a movable member relative to a stationary member. More particularly, the present invention relates to restraining mechanisms for adjustable tables.
2. Description of the Invention's Background
There are many situations where a movable member is movable relative to a stationary member. For example, in many adjustable work tables such as adjustable tool or vise tables there are often provided at least one base portion and at least one table portion which are movable relative to each other. Generally, a tool or vise is attached to one of the base and table portions. In the case of a tool, some type of workpiece guide surface is attached to the other of the base and table portions, and relative movement between the base and table portions thereby causes relative movement of the tool relative to the workpiece guide surface, and allows different positionings of the tool relative to a workpiece. For example, it is common in miter saws for base and table portions thereof to be rotatable relative to each other, and thus for the saw to be rotatable relative to workpiece guide surfaces thereof to allow miter cuts of various angles to be made with the saw.
In the case of a vise or clamp, the other of the base or table portions is fixed to a stationary object, such as a bench. Relative movement between the base and table portions then allows different positionings of a workpiece held by the vise or clamp relative to the bench.
In the situations where there is a movable member movable relative to a stationary member, it is often desirable to releasably restrain relative movement of the movable and stationary members. Thus, for example, in a miter saw, some mechanism for releasably restraining relative movement of the base and table portions is desirable, to hold the saw and the workpiece guide surfaces fixed relative to each other during cutting of a workpiece.
Many mechanisms have been proposed to effect such releasable restraint. For example, U.S. Pat. No. 4,011,782 to Clark, et al., discloses a locking and detenting portion for a power miter saw which includes a trigger latch member mounted on a swinging lever, which trigger pivots about a pin and includes a detent lug. A compression spring biases the trigger to urge the detent lug into any one of a number of recesses in a base front flange portion. A handle is additionally provided which can be threaded inwardly to force a vertical flange of a plate against the flange portion to secure the saw at angles other than and between those determined by the recesses 128.
There are several disadvantages to the arrangement described in the Clark, et al. patent. First, the trigger is only effective to latch a saw at certain preset angles. It does not provide a continuous range of angles at which the saw may be set. The handle provides such a continuous range, but requires that an operator must supply the force to frictionally secure a saw at a particular angle. The handle thus has the disadvantage that it requires an operator to supply a relatively large amount of force each time the operator wishes to secure a saw at a particular angle, and, in addition, that even the maximum amount of force which the operator can supply still results in a relatively weak frictional force, thus increasing the risk that the saw will move relative to a workpiece during a cutting operation.
Other devices are known Which include the same disadvantages as the handle of the Clark, et al. patent. For example, FIG. 9 of U.S. Pat. No. 5,060,548 to Sato, et al. illustrates a grip which is mounted to a rotatable turntable and which is threadable into frictional engagement with a side of a base, to thereby restrict rotation of the turntable. U.S. Pat. No. 4,527,453 to van Hauten discloses means to fix a saw table and saw unit relative to a fence, which includes bolts mounted in the fence. The bolts include sloped annular shoulders which mate with sloped annular shoulders in the fence such that turning of the bolts causes annular end faces of the bolts to be pressed against the saw table. FIGS. 6-10 of U.S. Pat. No. 5,189,937 to Garuglieri discloses a circular saw arrangement which includes a clamping lever which is rotatable to apply a load to an angular lever through a clamping bolt, and thence to the angled section of a screw bolt. The angled section thereby abuts against a projecting area of a guide-rib section of a table plate.
Each of the aforementioned devices includes a continuous range of angle settings, but requires an operator to apply a relatively large force to move a part into frictional engagement with another part. In addition, a maximum force which an operator can exert still generates only a relatively small frictional engagement force. In an apparatus that includes a high speed power tool which generates constant vibrations, it is undesirable to rely upon such a relatively weak force to prevent relative movement between a saw and a workpiece.
U.S. Pat. No. 766,791 to Richards discloses a locking mechanism for a miter saw, which includes a plug having a bearing face thereon for bearing upon a bearing face of a frame of a miter box. The plug is cut away to accommodate a rotatable rock shaft, which rock shaft is embraced by split hubs of a bow-shaped lever. The lever is biased by springs to bias the bearing faces into frictional engagement. The miter box of the Richards patent thus includes a continuous range of angle settings, and it also provides spring biasing so that an operator does not need to supply the force to frictionally engage two parts to secure the miter box at a particular angular setting. However, the frictional force supplied by the spring biasing of the Richards device still tends to be relatively weak, because the spring biasing is supplied through the same part, i.e., the lever, which an operator must move to release the frictional engagement. The larger the spring biasing force becomes, the larger the force the operator must supply to release frictional engagement. The spring biasing force can therefore not be too large or the operator will be unable to release the frictional engagement. In addition, the device of the Richards patent has the disadvantage that both spring biasing and releasing of frictional engagement are achieved through the lever, thereby through the rock shaft, and thereby through the plug, which unnecessarily increases the complexity and risk of failure of the device.
In view of the above, it is an object of the present invention to provide an improved restraining mechanism for releasably restraining movement of a movable member relative to a stationary member.
It is another object of the present invention to provide a restraining mechanism which can restrain movement of a movable member relative to a stationary member over a continuous range of relative positions of the movable and stationary members.
A further object of the present invention is to provide a restraining mechanism which does not rely upon an operator to generate a restraining force thereof.
Yet another object of the present invention is to provide a restraining mechanism that provides a relatively strong restraining force, but requires an operator to supply a relatively weak releasing force.
It is a further object of the present invention to provide a restraining mechanism which is relatively simple in operation and relatively resistant to failure.